Conditions under which servicing of military aircraft in theaters outside the United States must be accomplished differ so greatly from service conditions at home as to require quite different planning on the part of aircraft service organizations than has been previously necessary under domestic peacetime conditions.
Services, facilities, technical personnel and information which, in domestic operations are taken almost for granted, are largely lacking in many overseas theaters. This places a major responsibility both on the aircraft manufacturer and the Army Air Forces engineering and service personnel at home as well as on the corresponding civil and military personnel overseas. Full recognition and understanding of the actual conditions under which overseas service operations must be performed is of the greatest importance to full utilization and effectiveness of our far flung forces. The authors have been closely associated with engineering and service operations (particularly as applying to aircraft power plants) and have had opportunity to observe at first hand (in cooperating with the AAF and RAF) actual field service conditions in most of the Allied overseas theaters as well as at the many transit bases en route
One condition not fully appreciated is that overseas service operations in many cases must be performed under the most primitive conditions. This is particularly the case at advanced fighter bases. One must visualize conditions equal to or more difficult than those encountered back 20 years in the early "barnstorming" days to obtain a comparable picture of the lack of service facilities faced by overseas maintenance personnel at some of the advanced fields, particularly at times when "fronts" are moving rapidly. Under these conditions service facilities are of necessity extremely limited. Even ordinary hand tools are frequently not sufficiently available. Special tools and service equipment which at home would be considered indispensable are in many cases totally lacking. There are often no spare parts stocks on which to draw except by "cannibalizing" other grounded aircraft. This practice of robbing grounded aircraft of needed spares has in many cases attained the status of standard practice at many advanced air bases. Most urgently needed spares are frequently flown in from supply bases. Any new or unexpected parts requirement, however, may exhaust the immediately available supply and necessitate grounding of equipment until spares can be flown in. It is under this condition that "cannibalizing" occurs. Once grounded for lack of minor spares aircraft are frequently stripped so rapidly as to become permanently immobilized unless returned to bases at the rear for overhaul. In many cases where advance fields are supplied principally by air these salvage operations are impossible.
A brief description of one of the air bases located on the desert in the Middle East, which was visited by the authors, will serve to further illustrate conditions under which fighter aircraft have been required to operate and the difficult conditions under which service and overhaul operations must frequently be performed. This fighter base was simply a flat desert area approximately three miles in diameter with no prepared runways or hard surface. It had been used as an advanced Allied fighter base at the time of Rommel's last push on Cairo (summer of 1942) and at the time of the authors' visit was being used as a squadron formation and advanced trainer base. Numerous RAF and AAF squadrons were dispersed round the edge of the designated landing area. there being little to distinguish the field from the surrounding desert area except the parked aircraft on the ground and the scattered tents which constituted the only housing for personnel. There was no housing for planes or equipment, everything being spread around in the open.
During the winter months occasional rains tend to harden the sub-surface, leaving a loose dust layer on top which is one to four inches deep. This condition becomes much worse during the summer months. This top surface is made up of various particle sizes ranging from ordinary sand particles to material as fine as talcum powder.
Two jeeps comprised the total of ground transport facilities at this field at the time of our visit, so that planes were frequently being taxied across the field for purely transport purposes. One general repair truck was available at that time, the only other tools being those brought in by maintenance personnel in their own kits. One of the first requests made of us was to see that more hand tools were provided. Even tool kits originally shipped with planes had disappeared before equipment reached this point. No maintenance of spare parts stocks was attempted except for minor items such as spark plugs, gaskets, etc. New or overhauled engines were sometimes flown in and replaced but whenever possible ships were flown back to better-equipped bases, farther to the rear, for necessary service and overhaul. Often it was impossible to locate enough usable spares to get damaged aircraft back into the air for return to overhaul bases.
Dust exposure conditions in this theater were extremely bad during the entire year and presented many service difficulties.
Even though our trip was made during the winter season with dust conditions at a minimum, we started to encounter dust of serious magnitude on the trip north across Africa. At one of several transit fields used in ferrying ships across Africa, even though runways were black topped, the dust was blowing with a very light wind from extensive additional areas being developed by thousands of native laborers. The soil at this field was reddish in color, like iron ore, and extremely fine. It was encountered everywhere at this post, including the barracks and mess buildings some distance from the airport.
At this first desert field encountered on the trip out ― and from here on at all fields in the Cairo and eastern Libyan area― the soil and dust conditions are in varying degree distinctly desert in character. The soils at various fields vary as to the percentage of coarse material present but all are characterized by a relatively high percentage of extremely fine dust which is stirred up by the propellers and floats in the air for a substantial time even when no wind is blowing. Moderate winds when blowing keep the lower air levels well loaded with this extremely fine material. High winds create dust storms in which visibility is sometimes reduced to 10 feet in daylight. We did not see these conditions at their worst as rains during the winter season reduce the depth of the dry top surface and tend to provide a relatively hard base structure one to six inches under the surface.
The extreme fineness of a percentage of this surface dust is illustrated by several specific experiences. At one of the desert transit fields when we first arrived we sensed an irritation of the nose and throat even though the dust was not visible in the air at the time. We were told that nearly everyone at the station had "colds" which were attributed to this airborne dust. Later in the trip on one occasion following exposure to propeller blast, eyes several hours later started watering but without any indication of irritation. The following morning eyes were smarting and it was several days before the effects of this extremely fine dust were entirely eliminated. We were told of an experiment conducted by other representatives attempting to obtain samples of this fine dust, in which a small household electric vacuum cleaner with cloth filter bag was attached to the tail of a ship and operated during successive take-offs. After adequate exposure the bag was found only to contain a limited amount of coarse material. All of the fine dust had passed through the filter bag.
It may be readily appreciated from the foregoing details that exclusion of dust from airplane structures, especially engines, is practically impossible to accomplish. To completely exclude dust one must exclude air, under desert conditions. As this is a physical impossibility, the urgency of adequate air cleaner equipment at all engine openings is obvious.
During the dry season, when the dust conditions in the desert are at their worst, high winds occasionally arise which create dust storms which carry this dirt to great heights. Reports of limited visibility due to dust at altitudes from 10,000 to 12,000 feet are not uncommon during these storms. Conditions near the ground are extremely bad with visibility so poor that it is often unsafe to move about in camp. Instrument take-offs from desert fields are not an uncommon requirement even with moderate wind conditions. Dust, once stirred up by aircraft or motor transport, will sometimes hang for hours in the air.
Protection of engines from dust during operating is only one phase of the service problem. Equally if not more important is the protection of all engine openings while aircraft are on the ground. This is especially difficult due to the large size of some of the desert fields and the military necessity for wide dispersal of equipment. Fighter aircraft in general have a much greater exposure to dust than bombers. The latter types, particularly the heavier equipment, have in general been operated off of fields with some form of paved or bituminous runways. Weight of the equipment makes this necessary. Engine locations in bombers are in general higher off the ground and less exposed to dust thrown up by wheels in taxiing. The fighter, because of lighter weight, can be and is usually based on fields without runways, at more advanced positions with less service facility than the bombers and is actually exposed to dust conditions much more severe than is generally true for the bomber. Also, another dirt exposure to which the fighter is submitted, not common to the bomber, is the alert warm-up which has frequently been done for five minutes out of every half hour of daylight. The bomber may only have one mission daily or at night, and is then only exposed to this warm-up practice once or twice daily. Fighters on alert cannot be protected when not running. It should be noted that the operating hours records make no showing of ground running time so that none of this alert operation appears in operational hours. Engine life history in these two types of service reflect this difference in exposure and operating condition. The result is that fair comparisons of durability between engines of different makes and types cannot be drawn unless made for the same type of service and with equal air cleaner protection.
Service conditions in other theaters are not necessarily as severe. Facilities at semi-permanent bases are rapidly being improved and expanded and many are quite extensive. However, the conditions at advanced fighter fields wherever a front is moving, requiring frequent moves from one field to another, will of necessity involve a serious lack of service facilities, equipment and supplies.
One of the outstanding conclusions reached as a result of overseas field service observations, is that everything possible must be done in the design and engineering of aircraft to insure ease of service and maximum durability under the most primitive field conditions. Even though minimum weight is paramount, especially in the case of fighter aircraft, some weight increase even with fighters, and more so with bombers, is justified if it results in easier, more rapid servicing in the field or contributes to greater durability of engines such as obtained with effective dust protective equipment.
Latest figures from one important major theater show bombers even with well organized ground facilities to be in the air only about three per cent of the total time. Comparable figures for fighter equipment are not available but probably are not too much better. The greatest, single factor reported as responsible for this low percentage is the difficulty of keeping up necessary service operations and repairs. Well-informed observers point out that designers should be guided to a far greater extent than at present by the primary necessity for quick and easy servicing. It appears particularly necessary that aircraft be designed so that they can readily be broken down into units, each complete in itself, and of such size as to be easily handled on standard transport vehicles; and so that a minimum of time is required to remove any given unit and replace it with a new or overhauled assembly. Even though such construction is somewhat heavier it should be pointed out that the increased percentage time in the air makes up many times over for the slight increase in weight and decreased bomb load which can be carried. Total weight of bombs delivered per month or per year is what is really important, not the weight of bombs per trip. Consider the following: Two different types of aircraft construction, one of which in general can be separated readily into numerous, easily handled, completely equipped sub groups, each of which can be serviced and repaired as independent sub-assemblies; compared with the other common type construction which consists of a smaller number of larger assemblies comprising in effect a single main unit structure, once assembled, in effect tied together by wiring harness, hydraulic lines, etc., and thereby not capable of easy, quick disassembly in small portable units. Experience has shown that even though the former type construction is heavier and carries less bomb load per trip, that its bomb load per month or year is far greater than the latter type, due to the greater percentage of time spent in the air and the greater number of missions completed.
The argument in favor of designing for easy service replacement of relatively small self-contained sub-assemblies is possibly best made by visualizing the case of a bomber which has made a forced landing on a farm field. In the first case service crew and trucks arrive, disassemble the ship into units, transport them on special truck back to base where damaged units are exchanged for shop-overhauled units and the ship is back in the air again in a matter of days. In the case of the integral type construction suffering similar forced landing a complete service unit, including portable repair truck, arrives, sets up camp, proceeds under great difficulties to repair the damage on the spot with the limited facilities available. This operation may require many weeks during which time a runway has also had to be prepared so that the ship can subsequently be flown out and back to base.
Portable field repair facilities at their best cannot compete with permanent unit overhaul shops either in quality or quantity of work turned out. Lack of skilled personnel also dictates that overhaul be carried out at fixed base shops, each specializing in the reconditioning of a given unit or type of equipment where a limited number of skilled supervisors can direct the work of large numbers of relatively unskilled people.
As an illustration of the extent and magnitude of the field service overhaul problems which have to be met, facts and figures obtained in the Middle East should be considered.
During the period from June 1941, to December 1942, RAF in the Middle East theater alone at semi-permanent overhaul bases in the Cairo area overhauled or rebuilt 4,946 complete aircraft of all types and 7,929 engines of 16 different makes or models. By early December, 1942, these overhaul facilities had been expanded on the basis of overhauling largely from previously salvaged material, until the repair rate on aircraft was approximately 500 per month and the repair rate of engines was approximately 1,000 per month. These figures in relation to the size of the air operation for the middle east area will give only a general idea of the magnitude of the service and overhaul problem with which we are confronted in all other theaters and points up the argument that design for easy service is of primary military importance and should be given far greater emphasis by designers and procuring agencies than at present.
One of the greatest difficulties encountered in overseas service operations is the general lack of spares in advanced theaters at the places needed. This does not necessarily mean that sufficient spares have not been manufactured and shipped overseas. Thousands of tons of spares have actually been shipped, but in too many instances shipments have not reached their original intended destination. Even when badly needed spares have been shipped by air they frequently are unloaded en route in favor of high priority passenger movements and are then likely to lay over at any one of the many transit points until special arrangements are made for their continued movement. Whenever personnel and materiel must compete for air transportation which is operating beyond its capacity limit, the materiel comes out second best. Personnel can argue for travel priority, materiel cannot, and frequently fails to move until followed up by special expediters assigned to that problem. Separate flight schedules for personnel and materiel would, with rigid restrictions governing encroachment of one service upon the other, accomplish much to correct this difficulty.
Another difficulty is that during periods when materiel in transit is unloaded it frequently is pirated by local supply personnel who find themselves in immediate need of the materiel in their hands. The human tendency to acquire materiel not needed immediately but which is thought to be possibly needed later must also be reckoned with, especially when the paper work necessary to the tracing of overseas shipments is as loosely handled as is the case during war time.
Shipments originally destined for one theater are sometimes diverted en route to another under the pressure of military necessity. In some cases materiel whose urgent need in one theater is not fully appreciated by transport personnel at intermediate transit bases is indefinitely delayed by not being given sufficient priority to insure prompt movement.
Another major problem exists even after materiel has been transported to its intended destination. It frequently becomes "lost" due to the normal circumstances surrounding the necessary methods of handling at the destination. Unpacking and warehousing in overseas theaters is the exception rather than the rule. Only at well protected overhaul bases remote from the active theater is it in general practical to bin this materiel. In areas exposed to possible air attack by the enemy extensive dispersal of materiel to insure against loss from bombing is a military necessity. This means that warehousing and binning even if such facilities were available would be impractical. In general, under this condition spares must be stored often in the open, in their original shipping containers and usually scattered over considerable areas. During handling in transit or storage exterior markings identifying contents of individual boxes or containers are frequently effaced so that identity of contents is lost. If boxes are opened for inspection materiel will usually be damaged by exposure unless again conditioned for storage. Sufficient personnel and facilities for the latter are usually not available. The overall result of this combination of circumstances is that spares are often "lost" through inability to locate the specific parts needed in the "dispersed supplies."
Some improvements in this general situation are of course now being effected. Improved methods of packaging and identifying for overseas shipments are being put into effect and in some cases spares are being shipped in screw top boxes, which can be converted to bins. Better methods of preparation for storage are being worked out to insure against parts being damaged from exposure in transit. Reconditioning for storage upon arrival after opening of packages will also be of great help. Conditions at the major overhaul bases in areas now reasonably safe from air attack are in general fairly well organized. Much remains to be done in improving the spare parts situation at the more exposed advanced bases.
The necessity for extensive servicing of aircraft at front line fields under the most difficult supply conditions is not as fully realized in this country as in the overseas theaters. This is especially true in the southwest Pacific theater. Many times equipment cannot be returned to overhaul bases unless it can be rendered flyable, because other transport facilities are not available. In the Middle East and North African theaters wrecked aircraft could be trucked back to overhaul bases when not flyable.
In the southwest Pacific theater the service problem is one step further removed from the builder's plant and greater dependence on front line service and salvage operations in lieu of many new spares appears necessary to most effective prosecution of the war. It is the authors' suggestion in view of those observations that aircraft, engine and accessory manufacturers actively undertake a program directed toward developing salvage procedures which require only simple, readily portable hand tools which can be utilized under first echelon conditions.
Greater recognition of this phase of the service problem and further assistance in the matter of recommended salvage procedures and suitable hand tools is most urgently needed by operating personnel.
Greater attention should be given to power plant installations from the service-time standpoint. It takes much too long to change an engine in any of the current installations. If some of our installation designers were more familiar with the actual service operations in the field new designs would be greatly improved.
Power plant installations must be designed to withstand any amount of humidity and any amount of dirt. In the latter case, dirt protection while aircraft are on the ground has been especially neglected. Carburetor air cleaner equipment should be fully automatic in action. Pilots are not sufficiently conscious oi its importance or interested in overall life of engines to be depended upon for satisfactory manual operation.
Despite the humidity factor electrical equipment gives far less trouble in service than hydraulic equipment. The authors have never talked to a crew chief who would not prefer everything electrically to hydraulically operated. Hydraulic leaks are common and difficult to correct in the field.
It is suggested that all new service types be given a service test on a rough field, with plenty of dust and high humidity and by completely green ground crews. Limit cards should also be removed as these have no meaning in the war zone until the pilot has had the personal experience of having something fail if a given limit is exceeded. If installation designers were to work to such a service test, rapid improvements in field serviceability would result.
This article was originally published in the January, 1944, issue of Flying magazine, vol 34, no 1, pp 54-56, 106, 111.
The PDF of this article includes photos of an A-20 and a Jeep in a sandstorm and of maintenance techs working on an Allison from a P-38.
Photos credited to US Army Air Forces, Acme Newspictures, General Motors.